Frequency Stability Analysis of the Nordic Power Systemwith New Hydropower Governor Settings

Abstract: The Nordic power system is under continuous development. New productionsources and loads are installed at a high rate and old ones are taken out of operation.This development gradually alters the power system dynamics. The NordicTransmission System Operators (TSOs) have observed that the frequency qualityis gradually decreasing and recognized a number of reasons for this. Theautomatic frequency containment reserve (FCR-N) is in place to keep the electricfrequency within the interval 50 +/- 0.1 Hz during normal operation. Thisfunction is mainly provided by a number of hydropower plants where the turbinegovernor is set to control the discharge in proportion to the measured frequencydeviation. In later years it has been shown that the disturbance damping is verylow in an interval around 1/60 Hz and it is believed that proper tuning of theturbine governors that provide FCR-N can help mitigating this problem. Newregulator settings have been suggested in a recent study performed at Vattenfalland Uppsala University to improve the performance of the FCR-N, yet keepingthe system robust and the wear on participating units at a minimum. It is nowdesired to investigate the possible eects of new governor settings on the overallpower system stability. This thesis work consists of three main parts. First of all, a reduced Nordicpower system model is constructed in Simpow and validated with PMU datafrom the TSO. Secondly, the frequency responses with the newly suggestedgovernor settings have been investigated when introducing a disturbance into thesystem. Thirdly, the eects of the new governor settings on electro-mechanicaloscillations are investigated. In a word, the overall performance for new governorsettings are tested in a large scale power system model in this thesis work.